FLASH KINETIC SPECTROSCOPIC STUDIES OF DINUCLEAR RHODIUM(I) COMPLEXES

Excitation of concentrated acetonitrile solutions of [Rh(tol)4]PF6 (tol is p-methylphenyl isocyanide) at 562 nm, where strong absorption attributable to [Rh2(tol)g]2+ occurs, produces emission (λmax 697 nm) with a quantum yield of 0.0065 and a lifetime of ≤2 ns. Excitation of [Rh2(bridge)4](BPh4)2 (bridge is 1,3-diisocyanopropane) in acetonitrile solution at 553 nm gives emission at 656 nm with a quantum yield of 0.056 and a lifetime of ≤2 ns. The emission is assigned to 1A2U⇄1Alg (2a1g⇄la2u) in both dinuclear Rh(I) complexes. Excitation also gives rise to long-lived transient absorptions attributable to the following dinuclear and trinuclear species: ~8 μs, Rh2(bridge)42+; 0.09 μs, [Rh2(tol)8]2+; and 0.14 μs, [Rh3(tol)12]3+. In the dinuclear complexes, this transient is most likely 3A2u, which is the triplet excited-state partner of1A2U. The results suggest that the spin-orbit components of 3A2U possess very little singlet character. © 1978, American Chemical Society. All rights reserved.